/Engine/Plugins/Online/OnlineSubsystem/Source/Public/Interfaces/OnlineUserInterface.h
Contacts server to obtain user ids from external ids
true if the operation was started successfully
bool QueryExternalIdMappings ( const [FUniqueNetId](API\Runtime\CoreOnline\Online\FUniqueNetId) & UserId, const [FExternalIdQueryOptions](API\Plugins\OnlineSubsystem\Interfaces\FExternalIdQueryOptions) & QueryOptions, const [TArray](API\Runtime\Core\Containers\TArray)< [FString](API\Runtime\Core\Containers\FString) > & ExternalIds, const [FOnQueryExternalIdMappingsComplete](API\Plugins\OnlineSubsystem\Interfaces\IOnlineUser\FOnQueryExternal-) & Delegate )